"Mr. Armstrong has 10 days to respond to USADA's official charging letter, which was sent Thursday evening, to decide whether to contest the charges. If he does, the case will be argued in front of an independent arbitration panel of three people. To prove its case, USADA would have to convince two arbitrators that the allegations are true.

"Robert Luskin, an attorney for Mr. Armstrong, said Friday the decision to charge Mr. Armstrong with doping violations is 'wrong' and 'baseless.' He said the charges are the result of the agency's 'toxic obsession with Lance Armstrong' and that there 'is not one shred of credible evidence" to support them.'"

Armstrong took to Twitter to criticize the anti-doping agency. He wrote: